What City Life Does to the Country Mouse

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White Footed Mouse

Living in the big city changes you. From the air we breathe to the landscape we navigate to the food we eat, metropolis-dwellers respond to urban circumstances with adaptive behaviors.

And it turns out, these changes can go gene-deep much faster than anyone thought possible.

"Pests, mosquitoes and weeds have evolved all sorts of resistance to all sorts of things that we use to kill them," said Dr. Jason Munshi-South, an associate biology professor at Fordham University. "Even rats in New York City are partially resistant to the rodenticides we use against them. And that all happened in a matter of years, and not hundreds of thousands, or millions of years."

He says there are three main ways that animals will adapt.

The fastest and most obvious way is by changing behavior, such as altering diet or feeding times. Raccoons, for example, may move from the more natural diet of their woodland counterparts to one that includes food scraps thrown out by humans, or even dog food left out for pets.

The second type of change is found among groups of animals that are geographically isolated, like rodents in parks. Random changes are accentuated by interbreeding and eventually lead to distinct genetic profiles over time.

The third category of adaptation, Munshi-South says, is the regular process of natural selection, but on a much more rapid timetable than previously thought possible. Animals with certain genetic variations thrive or reproduce more, leading those traits to get passed on more widely throughout a population.

"It happens on the timescale of years rather than decades or hundreds of years or hundreds of thousands of years," he said.

The white footed mouse, for example, has roamed in this area since long before there was a New York City. But as the dense woods they lived in became a concrete metropolis, Munshi-South says their metabolism has changed to be able to digest food that was available, such as the brush beneath trees.

"It's really sort of a survival of the fittest," he said."They either survive in this modified landscape, or they don't."

Hypothesis is written and produced by Alec Hamilton and edited by Matthew Schuerman. Sound design and engineering by Liora Noam-Kravitz. Original music by Josh Burnett.